Can the material on the surface affect camera's thermal readout?
Yes,
definitely! And bare metal is among the worst affected materials -- it reads _much_ cooler than actual. You can coat it with black spray paint or spray-on boron nitride to bring the surface emissivity closer to what the imager assumes. Or, if you have an imager with adjustable emissivity assumption, set it to 0.02 or so and look only at the gold plated surfaces.